This invention relates to master alloys. More particularly, this invention relates to a master alloy made using non-spherical aluminum particulate as a binder for a non-compactable metal particulate.
In the production of alloys, such as an aluminum base alloy, it is customary to add the alloying metal in a concentrated form sometimes referred to as a master alloy. Thus, for example, to provide an aluminum base alloy containing 2 wt. % manganese, a master alloy containing from 50 to 80 wt. % manganese may be added in the proper proportions (depending upon the manganese content of the master alloy) to smelter grade aluminum to obtain the desired aluminum base alloy. The use of master alloys, i.e., an alloy containing both the principal alloying metal and another metal, such as aluminum, as additives to a molten metal, such as molten aluminum, is made to assist in rapid dissolving of the additive in the molten metal without significant cooling and solidification of the molten bath.
Brown et al, U.S. Pat. No. 3,592,637 describes the use of finely divided mixtures of the alloying metal, referred to as a principal material, and a second metal, referred to as a promoter material, to provide a more rapid dissolving of the added materials in the molten metal bath. The patent points out that the addition of the alloying metal by itself in the form of a finely divided metal powder, such as manganese powder, would be satisfactory. However, it would present difficulties in penetrating the dross on the top of the aluminum, as well as resulting in possible oxidation losses of the manganese. Additionally, there can be dusting and pyrophoricity problems if powder was used. The patent, therefore, provides for the use of pellets formed by pressing powdered mixtures of the principal metal and the promoter metal (e.g., manganese and aluminum).
However, the formation of such pellets of briquettes using finely divided powders can itself introduce pyrophoricity problems in the formation stage of such pellets or briquettes. For example, when finely divided aluminum powder is used as the additional ingredient mixed with the principal metal of the mixture, the finely divided aluminum powder must be carefully handled to prevent uncontrolled oxidation. Furthermore, it is known that finely divided spherical particles do not compact well, thus necessitating the use of a binder to aid in cohesion of the particles which, in turn, adds to the cost of the process.
It is, of course, also known to form sintered particles from finely divided particulate which may be nonspherical. For example, Malard U.S. Pat. No. 4,252,577 discloses a process wherein metal scrap cuttings are used to make sintered pieces by cleaning, grinding, heat treating and sorting metal scrap cuttings.
While pellets or briquettes of master alloys could be formed by sintering, the additional expense involved in forming a sintered product merely as a transitory master alloy form to aid in formation of an aluminum alloy is not justifiable.
In some instances, the master alloy may be formed into a briquette merely by compacting non-spherical particles. However, some alloy materials, such as, for example, manganese, are brittle and friable materials, i.e., non-malleable, and will not compact but rather merely crumble, even though non-spherical particles are utilized. The usual practice, therefore, is to use a binder, such as an organic binder, which will burn off as the master alloy briquette is introduced into the molten metal mass. While this is less expensive than a sintering process, it still involves extra cost, the avoidance of which would be economically advantageous.